Chapter 13: Evidence of Evolution - Vocabulary Flashcards

Overview

  • Chapter 13: Evidence of Evolution
  • Topic focus: how we test and document evolution using multiple lines of evidence
  • Learning objectives (Ch. 13, sections 13.1 - 13.6):
    • Explain what different lines of evidence can tell us about evolution
    • Explain how the fossil record and isotopes can shed light on the characteristics of extinct life and contribute to inference of evolution and ecology
    • Explain how we use biogeography, homologies, vestigial structures and convergent evolution to document evolutionary change and possible lineage relationships
  • Core idea: Species we see today are snapshots of an ongoing evolutionary process; life on Earth began long ago and has changed through time under geological influence and ecological pressures
  • Key framing: the geologic timescale is used to organize Earth history around biological and geographical events

The Evolutionary Process: A Snapshot View

  • Concept: Species today are not static; they represent moments in a long, branching process of evolution
  • Visual takeaway: Evolutionary history is a continuum, with surviving lineages and extinct lineages contributing to present diversity

The Geologic Context and Origin of Life

  • Life on Earth arose approximately 3.8 ext{ billion years ago}
  • Scientists use the geologic timescale to divide Earth’s history into eons and eras, based on evidence of biological and geographical events
  • Evolutionary events are studied in the context of this geologic timescale, linking biology with Earth history

Fossil Evidence and Paleontology

  • Paleontology is the study of fossil remains or other clues to past life
  • Fossils provide the original evidence for evolution; they reveal what ancient organisms looked like and, in some cases, how they behaved
  • Fossils show both form and function (evidence of behavior through trace fossils, trackways, etc.)
  • Fossils in Colorado have yielded large surface deposits (scrapes up to 2 meters in diameter) illustrating paleoenvironments
  • Fossils help infer lineage relationships and ecological contexts across deep time

Fossil Formation: How Fossils Are Made

  • Fossils form in multiple ways:
    • Compression and petrification (permineralization) — often preserves hard parts in stone-like form
    • Impressions and casting — external mold of an organism or internal cast filling a mold
    • Intact preservation — rare, when organisms are buried rapidly in low-oxygen conditions, minimizing decay and scavenging
  • Example sources and figures referenced: Section 13.2, Figure 13.4; images credit for specimens and contexts (various sources)
  • Illustrated examples include: ancient remains trapped in amber, dinosaur feathers preserved, and micro-contexts like preserved trace materials
  • Important rationale: The mode of preservation affects what information is recoverable (external shape, internal structures, soft tissues rarely preserved)

Fossilization in Practice: Conditions and Manifestations

  • Intact preservation occurs when burial is rapid and oxygen is scarce, limiting decomposition and scavenging
  • Fossilization can capture details such as skin impressions, feather imprints, and even preserved soft tissues rarely; most fossils are of hard parts
  • Notable examples mentioned include: snakefly preserved in Baltic amber (~34–48 million years ago), dinosaur feathers preserved in Myanmar (~160 million years ago), and other preserved specimens
  • Fossils also reveal behavioral clues through associations and arrangements that suggest social or mating behaviors (e.g., dinosaur–bird-like displays)
  • Fossils in Colorado illustrate large-scale trace evidence (scrapes up to ~2 meters in diameter), indicating behavior or habitation patterns

Fossil History and Its Incompleteness

  • Fossil history is incomplete for several reasons:
    • Many organisms have soft bodies that fossilize poorly or not at all
    • Erosion, fossil burial, and plate tectonics can destroy or relocate fossils over time
  • Oklahoma marine fossils indicate historical ocean coverage in areas that are now terrestrial, illustrating shifts in environments through time
  • The incomplete nature of the fossil record is a recognized limitation in reconstructing full evolutionary histories

Ideal Sequence for Fossilization (The Path to Becoming a Fossil)

  • The typical sequence proposed for fossilization involves:
    1) Die in a promising location
    2) Avoid being consumed
    3) Become buried by sediment
    4) Survive through time
    5) Be exposed and then found (before eroded)
  • Note: Most organisms never fossilize due to various ecological and taphonomic factors; fossil records reflect a biased sample of past life

Dating Fossils: Timing the History of Life

  • Dating methods yield clues about when organisms lived and changed
  • Relative dating:
    • Dates fossils according to the rock layers in which they are found
    • Assumes deeper layers are older than those above them; indirect and less precise, but valuable
  • Absolute dating (radiometric dating):
    • Dates the fossil using the chemistry of surrounding materials or the fossil itself
    • Example method: radiometric dating by measuring the amount of ^{14}\mathrm{C} in a fossil to estimate time since death
  • The combination of relative and absolute dating helps place fossils within the geologic timescale and infer rates of evolution

Isotopes and Diets: What Carbon Isotopes Tell Us

  • Carbon isotopic signatures are used to infer diets of extinct species
  • Isotopic analysis can reveal trophic level, feeding strategies, and ecological niches of ancient organisms
  • This evidence complements morphological data to reconstruct past ecologies

Biogeography: Geography, Plate Tectonics, and Evolution

  • Biogeography examines how species are distributed geographically and how geography shapes evolution
  • Earth’s geography has changed drastically over the last 200 million years; plate tectonics drives continental drift and ocean opening/closing
  • The theory of plate tectonics posits that forces within the planet move Earth’s land masses
  • Continents continue to move today; earthquakes and volcanoes attest to ongoing plate motion
  • Fossil and species distributions around 200 million years ago suggest the existence of a supercontinent named Pangaea
  • Biogeography helps explain historical connections and separations of lineages across oceans and landmasses
  • Wallace’s Line (a biogeographic boundary) illustrates long-term separation of fauna on either side, leading to distinct, independently evolving communities
  • These geographic patterns provide evidence for historical isolation and divergence among lineages

Anatomical Evidence: Shared Body Plans and Common Descent

  • Investigators examine anatomical features to infer evolutionary relationships between organisms
  • Homology: features derived from a common ancestor
    • Example: forelimbs of diverse vertebrates contain similar bone arrangements, suggesting a common ancestral limb structure
    • Key figure: Section 13.3, Figure 13.10 illustrates anatomical homology
  • Vestigial structures: reduced or unused features that are homologous to functional structures in related species
    • Examples: vestigial eyes in some blind mole species; hindlimbs in some snakes; pelvises in whales
    • These serve as evidence of evolutionary ancestry despite current function loss
  • Analogous structures: superficially similar structures that arise independently and are not from a common ancestor
    • Example: wings in birds and insects both enable flight but have different underlying structures
    • Section 13.3, Figure 13.12 highlights these differences
  • Convergent evolution: the process by which similar structures evolve independently in distantly related lineages due to similar selective pressures
  • Developmental homology: embryonic development often reveals deeper similarities than adults
    • Example: human and chimp skull development show greater similarity in fetuses than in adults
    • Section 13.5, Figure 13.14 demonstrates developmental homology
  • Early vertebrate embryos appear alike; adult forms diverge, making embryonic comparisons a powerful tool for inferring relationships
  • Example comparisons include chick, mouse, and human embryos (illustrations referenced in figure 13.15)

Molecular Evidence: DNA, Proteins, and the Language of Life

  • Molecular data provide extremely detailed insights into relatedness beyond morphology
  • Sequence similarities are inherited from common ancestors; two unrelated species are unlikely to evolve exactly the same DNA and protein sequences by chance
    • Section 13.6, Figure 8.4 introduces molecular homology concepts
  • Changes in DNA underlie evolutionary changes; gene-level events can drive adaptation
    • Example: amylase gene duplication associated with a high-starch diet shows how gene copy number changes can respond to ecological opportunities
    • Example image references: chimp and human contexts for amylase gene study
  • Homologous protein sequences demonstrate common descent across taxa
    • Cytochrome c is a mitochondrial protein found in all eukaryotes; the degree of amino acid differences between species reflects the distance from their common ancestor
    • Section 13.6, Figure 13.19 illustrates molecular homology using cytochrome c
  • Molecular clocks: mutations accumulate in DNA at a relatively constant rate over time when not strongly selected for or against
    • This underpins the concept that genetic differences can be translated into approximate divergence times
    • Section 13.6, Figure 13.20 illustrates the molecular clock concept

Integrating Evidence: How the Pieces Fit

  • Consilience of evidence across geology, paleontology, geography, anatomy, development, and molecular biology strengthens inferences about evolution and lineage relationships
  • Fossil, isotopic, geographic, and molecular data collectively illuminate the history of life, the timing of major transitions, and the emergence of biodiversity
  • Ethical, philosophical, and practical implications: understanding deep time informs debates about human origins, our relationship to ecosystems, and the responsibility to study and conserve life on Earth

Key References and Figures Mentioned (by section)

  • Section 13.1: Intro to evidence of evolution; link to geology and fossils
  • Section 13.2: Fossil formation, fossilization processes, dating fossils; Figure 13.3, Figure 13.4
  • Section 13.3: Biogeography and anatomical evidence; Figures 13.7, 13.8, 13.9, 13.10, 13.11, 13.12, 13.13
  • Section 13.5: Developmental homology; Figure 13.14, 13.15
  • Section 13.6: Molecular evidence and clocks; Figures 8.4, 13.18, 13.19, 13.20
  • Notable empirical references mentioned: Lockley et al., Scientific Reports 2016 (dinosaurs dancing to woo mates); Greg Dale/Getty Images (fossil depiction); Terry Moore/Stocktrek Images/Getty Images (dating fossils); various image credits for fossils and embryos

Quick Recap: Core Concepts to Remember

  • The fossil record provides direct though incomplete evidence of past life and evolutionary transitions
  • Dating fossils uses relative layering information and absolute radiometric methods (e.g., dating via ^{14}\mathrm{C})
  • Isotopes, especially carbon isotopes, reveal past diets and ecological interactions
  • Biogeography links distributions to historical geologic events (plate tectonics, Pangaea, Wallace’s Line)
  • Homology (shared ancestry) vs. analogy (convergence) vs. vestigial structures clarifies relationships and evolutionary paths
  • Embryology often reveals deeper homologies that are not obvious in adults
  • Molecular data (DNA/proteins) provide high-resolution evidence for relatedness and timing via molecular clocks
  • The integration of multiple lines of evidence yields robust inferences about how evolution operates and how lineages are related